I currently dropped on Tanabe springs. I am satisfied with the front, but the rear is a tad to low for my liking. One side is slightly more lower than the other. I was thinking of leaving the front springs and swapping out the rear sprints for rear tanabe coilovers? Is this a sound option? Expense is a consideration; hence the reason not wanting to swap out the fronts.

 

Is your G RWD? If so I'd look in to Tein BasisZ coilovers, this newest version is no longer serviceable (shocks able to send to factory for rebuilding) so the price has dropped quite a bit, sets for under $500 shipped have been reported.
Here's one example, it doesn't list current G sedans but it fits them as well
Tein Street Basis Z Coilovers for the 370Z / G35 / G37 at KamiSpeed.com

 

Yes it's RWD. that link you provided has the min drop in front as 1.4. Lower than my current front drop on tanabes.

 

That's in the recommended range but the whole adjustment range is quite a bit more, here's the list, you would have room to go higher for sure, and just a little higher won't be a problem
TEIN USA | COILOVER KIT & SPRING KIT SEARCH ?INFINITI?G37 COUPE?2008+?STREET BASIS Z
You might shoot a pm to 4DRZ and see what he says as far as height range.

Also you could just use the rears and keep your front springs, that's what Rochester has w/ Swifts in front and Tein coils in back.

 

if u gonna do all that to the rears why not just put it in the fronts too and sell the tanabe springs as a set

 

all spring will sag more in the back. Only way is to go coilovers